Method of electronically correcting position errors in an incremental measuring system and measuring system for carrying out the method

Abstract

In the operation of an incremental measuring system, a measuring scale is scanned for generating periodic sinusoidal, analog measured-value signals. Digital countable signals are derived from the measured-value signals in conjunction with an electronic subdivision of the scale and are delivered to an electronic evaluating unit. Each countable signal is associated with a certain phase angle of the measured-value signals. For an electronic correction of position errors, predetermined signal levels are detected at a series of first points, which have an electrical spacing corresponding to a sub-incremental step constituting a fractional part of a scale increment, and these signal levels are alternatively detected at a series of second points, which have the same electrical spacing as the first points and are offset by a fractional part of this spacing, and in accordance with a correction program the measurement is selectively evaluated in response to the signal levels at these points so that corrections can be effected in steps corresponding to only a fractional part of such sub-incremental step.

We claim: 
     
       1. In a method of electronically correcting position errors in the operation of a incremental measuring system, in which a scanning unit is caused to perform a scanning movement relative to a measuring scale consisting of a multiplicity of scale increments and to scan said scale during said scanning movement to generate basically sinusoidal analog measured-value signal indicating the direction of said scanning movement,   said analog signals are electronically processed in a dividing stage to generate digital countable signals, which represent respective sub-incremental steps, which are substantially as large as fractional parts of one of said scale increments and are initiated at respective phase angles of said analog signals, which phase angles have a spacing which corresponds to said sub-incremental step,   said countable signals are counted in a sense depending on the direction of said scanning movement, and   the resulting counts are electronically evaluated,   the improvement comprising   defining additional phase angles between adjacent ones of said predetermine phase angles and offset from said predetermined phase angles by a predetermined fractional part of the spacing between said predetermined phase angles, and   evaluating the resulting counts electronically after a correction of said countable signals on the basis of selected ones of said additional offset phase angles whereby corrections are effected in fraction parts of the sub-incremental steps.   
     
     
       2. The improvement set forth in claim 1 as applied to the electronic correction of position errors in an incremental system for measuring lengths. 
     
     
       3. In an incremental measuring system comprising a scale member provided with an incremental scale consisting of a multiplicity of scale increments, a scanning unit operable to effect a scanning movement relative to said scale, to scan said scale during said scanning movement and to generate basically sinusoidal analog measured-value signals, which depend on the direction of said scanning movement,   dividing, trigger and pulse-shaping circuitry for receiving said analog signals and for generating digital countable signals in response to said analog signals, which countable signals represent respective sub-incremental steps, which are substantially as large as fractional parts of a scale increment,   counting means for counting said countable signals in a sense depending on the direction of said scanning movement, and   electronic evaluating means for evaluating the counts of said counting means,   the improvement comprising   electronic means for correcting position errors in the operation of the system, including at least two dividing circuits in said circuitry, which have taps having the same electrical spacing, which corresponds to said sub-incremental step, wherein said taps of each of said dividing circuits are electrically offset from the taps of each other one of said dividing circuits by a fractional part of said electrical spacing,   each of said dividing circuits is selectively operable to receive said analog signal and to present a trigger level signal at each of said taps,   additional trigger and pulse-shaping circuitry in said dividing, trigger and pulse-shaping circuitry for receiving said trigger level signals from said taps of said selectively operated dividing circuit and for generating said countable signals in response to said trigger level signals,   a selecting switch connecting a selected one of said dividing circuits to said electronic evaluating means, and   control means for controlling the operation of said selecting switch, said control means comprising a control logic arranged to prevent an operation of said selecting switch for initiating the operation of a given dividing circuit unless a countable signal has been generated in response to the operation of the currently operating one of said dividing circuits.   
     
     
       4. The improvement set forth in claim 3 as applied to a system for measuring lengths. 
     
     
       5. The improvement set forth in claim 3, wherein said circuitry comprises trigger and pulse-shaping circuits connected to the electronic evaluating means and said selecting switch is connected between said dividing circuits and said trigger and pulse-shaping circuit.   
     
     
       6. The improvement set forth in claim 3, wherein said trigger and pulse-shaping circuitry comprises a plurality of trigger and pulse-shaping stages associated with respective ones of said dividing circuits and   said selecting switch consists of a digital data selecting switch connected between said trigger and pulse-shaping stages and said counting means   
     
     
       7. The improvement set forth in claim 3, wherein said selecting switch is arranged to be operable in synchronism with the occurrence of a predetermined level of at least one of said analog signals. 
     
     
       8. The improvement set forth in claim 3, wherein said selecting switch is arranged to be operable in synchronism with a predetermined phase angle of one of said signals. 
     
     
       9. The improvement set forth in claim 3, wherein said counting means comprise a counter adapted to be preset to a selected count and arranged to receive and count said countable signals and   said selecting switch is arranged to determine another of said dividing circuits for selective operation in response to said counter assuming said selected count.   
     
     
       10. The improvement set forth in claim 9, wherein a temperature sensor for detecting the ambient temperature is provided and   said counter is arranged to be preset to a count depending on the ambient temperature detected by said temperature sensor.   
     
     
       11. The improvement set forth in claim 3, wherein a correction memory is provided, which contains correction data at a plurality of addresses, which are associated with respective positions of said scanning unit relative to said scale, and   said correction data are adapted to be retrieved from said memory and to be utilized to control the operation of said selecting switch.   
     
     
       12. The improvement set forth in claim 3, wherein said evaluating means comprise indicating means.